Fate and Persistence of a Pathogenic NDM-1-Positive Escherichia coli Strain in Anaerobic and Aerobic Sludge Microcosms

Abstract

The presence of emerging biological pollutants in treated wastewater effluents has gained attention due to increased interest in water reuse. To evaluate the effectiveness of the removal of such contaminants by the conventional wastewater treatment process, the fate and decay kinetics of NDM-1-positive Escherichia coli strain PI7 and its plasmid-encoded antibiotic resistance genes (ARGs) were assessed in microcosms of anaerobic and aerobic sludge. Results showed that E. coli PI7 decayed at a significantly lower rate under anaerobic conditions. Approximate half-lives were 32.4 ± 1.4 h and 5.9 ± 0.9 h in the anaerobic and aerobic microcosms, respectively. In the aerobic microcosms, after 72 h of operation, E. coli PI7 remained detectable, but no further decay was observed. Instead, 1 in every 10,000 E. coli cells was identified to be recalcitrant to decay and persist indefinitely in the sludge. ARGs associated with the E. coli PI7 strain were detected to have transferred to other native microorganisms in the sludge or were released to the liquid fraction upon host decay. Extracellular DNA quickly degraded in the liquid fraction of the aerobic sludge. In contrast, no DNA decay was detected in the anaerobic sludge water matrix throughout the 24-h sampling period. This study suggests an increased likelihood of environmental dispersion of ARGs associated with anaerobically treated wastewater effluents and highlights the potential importance of persister cells in the dissemination of E. coli in the environment during reuse events of treated wastewater.IMPORTANCE This study examines the decay kinetics of a pathogenic and antibiotic resistant strain of Escherichia coli in microcosms simulating biological treatment units of aerobic and anaerobic sludge. The results of this study point at a significantly prolonged persistence of the E. coli and the associated antibiotic resistance gene in the anaerobic sludge. However, horizontal transfer of the plasmid encoding the antibiotic resistance gene was detected in the aerobic sludge by a cultivation method. A subpopulation of persister E. coli cells was also detected in the aerobic sludge. The findings of this study suggest potential areas of concern arising from pathogenic and antibiotic-resistant E. coli during both anaerobic and aerobic sludge treatment processes.

Fate of Antibiotic Resistant Pseudomonas putida and Broad Host Range Plasmid in Natural Soil Microcosms

“…We observed a biphasic decay behavior of both P. putida KT2442 and RP4. This biphasic decay had been well documented in P. putida , E. coli and pathogens (Brouwer et al, 2017; Mantilla-Calderon and Hong, 2017). The concentrations of dsRed and gfp were average 1.3 × 10 8 and 4.3 × 10 7 copies g -1 dry soil after initial spiking event, and they slightly increased at first 2 days after inoculation, which might be due to the division of donor strains and was in accordance with previous studies (Elsas et al, 1989; Henschke and Schmidt, 1990).…”

Reusing Treated Wastewater: Consideration of the Safety Aspects Associated with Antibiotic-Resistant Bacteria and Antibiotic Resistance Genes

“…Specifically, antibacterial resistance carries a fitness cost that most often reduces growth rate and/or virulence [70,71]. However, there are some resistance mechanisms with little-to-no impact on growth rate and/or virulence [70], possibly because they are encoded in plasmids that share long evolutionary history and hence are highly stable in a particular bacterial host [72]. Occasionally, resistance even confers a fitness advantage [70,73].…”

Prevalence of Potentially Pathogenic Antibiotic-Resistant Aeromonas spp. in Treated Urban Wastewater Effluents versus Recipient Riverine Populations: a 3-Year Comparative Study

“…One of the main reservoirs of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) is wastewater treatment plants (WWTPs) (2). The high concentrations of bacteria coexisting with subinhibitory concentrations of antibiotics throughout the wastewater treatment process (2) provide optimal conditions enabling the development of resistance as well as persister cells, thus serving as vehicles of ARG dissemination in the environment (3,4). Although urban WWTPs provide several log reductions in bacterial populations in comparison to influents, treated effluents remain rich sources of multidrug-resistant (MDR) bacterial populations entering the recipient aquatic ecosystem.…”